Enantioselective Total Synthesis of (‐)‐Dehydrobatzelladine C.

2,2,5,7,8-Pentamethylchroman-6-sulfonamide. Following a general procedure, a solution of ClSO3H (46.3 mL, 227 mmol) and CH2Cl2 (290 mL) was added dropwise to a solution of 2,2,5,7,8-pentamethylchroman (47.1 g, 231 mmol) and CH2Cl2 (1.5 L) at 0 °C. Upon complete addition, the reaction mixture was allowed to warm to rt over 3.5 h. The reaction mixture was then quenched by pouring into saturated aqueous NaHCO3 (1.5 L). The layers were separated and the organic layer was washed with H2O (3 ¥ 1.5 L) and brine (0.5 L), then dried (MgSO4), filtered through a plug of silica and the filtrate was used directly in the following reaction. Ammonia was bubbled through the above solution of crude 2,2,5,7,8pentamethylchroman-6-sulfonyl chloride at 0 °C for 3 h. The reaction mixture then was filtered through a plug of silica gel, which was rinsed with EtOAc. The combined eluents were concentrated and the resulting crude solid was triturated with hexanes to yield 28.1 g (43%) of 2,2,5,7,8-pentamethylchroman-6-sulfonamide: mp 159–161 °C; H NMR (400 MHz, CDCl3) d 4.83 (s, 2 H), 2.65 (t, J = 6.9 Hz, 2 H), 2.56 (s, 3 H), 2.55 (s, 3 H), 2.13 (s, 3 H), 1.83 (t, J = 6.9 Hz, 2 H), 1.32 (s, 6 H); C NMR (100 MHz, CDCl3) 154.4, 135.5, 135.2, 131.2, 124.7, 118.4, 74.0, 32.6, 26.7, 21.4, 18.5, 17.4, 12.1; IR (KBr) 3424, 3286, 2974, 2933, 1560, 1459, 1320, 1146, 873 cm. Anal. Calcd for C14H21NO3S: C, 59.34; H, 7.47; N, 4.94. Found: C, 59.43; H, 7.46; N, 4.85.